1. Field of the Invention
This present invention is generally directed to the field of semiconductor manufacturing, and, more particularly, to a novel gas delivery system for various deposition processes, and various methods of using same.
2. Description of the Related Art
The manufacturing of integrated circuit products involves, among other things, the formation of layers of a variety of different types of material using a variety of different deposition processes, e.g., chemical vapor deposition (CVD), high density plasma chemical vapor deposition (HDPCVD), low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), etc. In some cases, these layers may be subsequently patterned by performing a variety of known photolithography and etching processes. In other cases, such layers may be formed to fill a previously formed trench-type feature. For example, as shown in FIG. 1A, a trench 12 may be formed in a semiconducting substrate 10 using any of a variety of known etching processes. The trench 12 may be formed in the substrate 10 as part of the process of forming a trench isolation structure that may be used to electrically isolate various integrated circuit components, e.g., memory cells, transistors, etc., from one another. The trench 12 will ultimately be filled with an insulating material, such as silicon dioxide, silicon oxynitride, etc.
As depicted in FIG. 1A, the trench 12 has a depth 14 (beneath the surface 11 of the semiconducting substrate 10) and a width or critical dimension 16. These dimensions may vary, but in current generation technology, the trench 12 may have a relatively high aspect ratio (depth/width) that exceeds approximately 4:1. For example, the trench 12 may have a width 16 of approximately 75 nm and the depth 14 may be approximately 200-600 nm. Simply put, as device dimensions for integrated circuit products have decreased, so have the dimensions of the trench isolation structures. Such reductions in the width 16 of the trench 12 are desirable for conservation of valuable plot space on an integrated circuit device.
Unfortunately, as the aspect ratio of such trenches 12 has increased, it has become more difficult to adequately fill the trench with the appropriate insulating material using existing processing tools and techniques. For example, as shown in FIG. 1A, using existing processing tools, a layer of insulating material 18, e.g., silicon dioxide, may tend to “pinch-off” in the opening of the high aspect ratio trench 12. This results in the formation of an undesirable void 20 in the trench 12. Such a void may reduce the effectiveness of the isolation structure when it is completed.
It is believed that this problem is at least partially due to the manner in which the gas delivery systems in modem deposition tools are configured. For example, FIG. 1B is a schematic depiction of an illustrative Applied Materials Ultima Model 5200 deposition tool. As shown therein, the tool 30 is comprised of a process chamber 32 and a wafer stage 34 that is adapted to hold a wafer 10 during the deposition process performed in the tool 30. The deposition tool 30 is also comprised of many additional components, such as a coil 31A positioned adjacent a top surface 32A of the process chamber 32, and a coil 31B positioned adjacent a side surface 32B of the process chamber 32. The coils 31A, 31B may be coupled to one or more RF power supplies 33 (only one of which is shown). An RF power supply 35 is coupled to the wafer stage 34. The tool 30 may also have other components, such as various electrical connections, temperature sensors, pressure sensors, mass-flow controllers, and valving which are well known to those skilled in the relevant art. Such components are not depicted so as not to obscure the present invention.
In general, a plasma 36 or glow discharge will be generated in the process chamber 32 by application of RF power to one or both of the coils 31A, 31B. Various reactant gases will be introduced for purposes of forming a layer of material on the wafer 10. For example, in the case of forming a layer of silicon dioxide, silane (SiH4) may be introduced into the process chamber 32. The silane may be mixed with a variety of carrier gases, e.g., hydrogen (H2), nitrogen (N2), argon (Ar), etc. In the Applied Materials tool 30, the vast majority of the process gas is introduced through a plurality of side nozzles 38 that are positioned slightly above the surface 11 of the wafer 10. The exact configuration and number of the side nozzles 38 will vary. For example, in one embodiment, eight groups of three of the side nozzles 38 are spaced around the perimeter of the process chamber 32. Each of the side nozzles 38 typically has an inside diameter of approximately 0.030 inches. Additionally, the Applied Materials tool has a single top nozzle 40 through which a relatively small amount of the total reactant gas flow is introduced into the process chamber 32. For example, the top nozzle 40 may have an inside diameter of approximately 0.030 inches and approximately 10-25% of the total silane gas flow may be introduced into the chamber via the top nozzle 40. As shown in FIG. 1C, the coverage area 42 of the reactant gas from the top nozzle 40 is only approximately 1-30% of the total area of the wafer 10.
As shown in FIGS. 1D and 1E, using existing gas delivery systems in modern deposition tools, there tends to be a variation in the thickness 44 of the process layer 18 near the edge region 45 of the wafer 10 as compared to the thickness 46 of the process layer 18 near the center region 47 of the wafer 10. This thickness variation may be significant in some situations. For example, the thickness variation may range from approximately 30-100 nm on a film having a target nominal thickness of approximately 300 nm.
Such thickness variations are due to a variety of factors that are believed to include the manner in which reactant gases are supplied to the process chamber 32. More specifically, there are two competing mechanisms involved during the process of forming the process layer 18—sputtering and deposition. In general, the deposition process involves a chemical reaction using the reactant gases supplied to the process chamber 32. Sputtering involves the action whereby ions generated by the plasma impact the layer of material 18 as it is being formed and, simplistically, sputter off portions of that layer 18 causing it to be deposited elsewhere. These processes continue to interact throughout the process of forming the process layer 18.
Unfortunately, due to the gas delivery system for existing process tools, the deposition mechanism tends to dominate in the edge region 45 of the wafer 10 due to the introduction of the majority of the reactant gases via the side nozzles 38. As a result, the sputtering mechanism is not as prevalent at the edge region 45 as would be desired. In some applications, such as the filling of high aspect ratio trenches, a higher sputter-to-deposition ratio is desired. Sputtering is desirable, at least to some extent, because the sputtering process tends to reduce the chances of pinching off the opening of the trench 12, as illustratively depicted in FIG. 1A.
Another prior art deposition tool 50, a Novellus Speed II Model, is depicted in FIG. 1F. As shown therein, the process chamber 32 of that tool has a generally dome-shaped top 41, a coil 43 that is coupled to an RF power supply 49, and it is provided with a plurality of upwardly-directed side nozzles 52. The number of side nozzles 52 may vary. In one illustrative embodiment, 3-50 of such nozzles 52 are spaced around the perimeter of the process chamber 32.
A problem still persists with respect to the ability to reliably and accurately fill trench-type features with high aspect ratios in the course of manufacturing modern integrated circuit devices. The present invention is directed to a method that may solve, or at least reduce, some or all of the aforementioned problems.